使用的是一個第三方庫android-pathview主要是一個自定義View——PathView，跟所有自定義View一樣，重寫了三個構造方法。並且最終呼叫三個引數的構造方法，在裡面獲取自定義屬性。

/**
     * Default constructor.
     *
     * @param context The Context of the application.
     */
    public PathView(Context context) {
        this(context, null);
    }

    /**
     * Default constructor.
     *
     * @param
 
 context The Context of the application.
     * @param attrs   attributes provided from the resources.
     */
    public PathView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    /**
     * Default constructor.
     *
     * @param context  The Context of the application.
     * @param
 
 attrs    attributes provided from the resources.
     * @param defStyle Default style.
     */
    public PathView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        paint.setStyle(Paint.Style.STROKE);
        getFromAttributes(context, attrs);
    }
 

檢視自定義屬性的xml，裡面共三個自定義屬性，pathColor為路徑顏色，預設值為綠色0xff00ff00，pathWidth為路徑寬度，預設值為8.0f，svg為路徑檔案

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="PathView">
        <attr name="pathColor" format="color"/>
        <attr name="pathWidth" format="float"/>
        <attr name="svg" format="reference"/>
    </declare-styleable>
</resources>

通過getFromAttributes函式獲得這些自定屬性，並賦值給成員變數，最後通過finally塊回收資源

 /**
     * Get all the fields from the attributes .
     *
     * @param context The Context of the application.
     * @param attrs   attributes provided from the resources.
     */
    private void getFromAttributes(Context context, AttributeSet attrs) {
        final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PathView);
        try {
            if (a != null) {
                paint.setColor(a.getColor(R.styleable.PathView_pathColor, 0xff00ff00));
                paint.setStrokeWidth(a.getFloat(R.styleable.PathView_pathWidth, 8.0f));
                svgResourceId = a.getResourceId(R.styleable.PathView_svg, 0);
            }
        } finally {
            if (a != null) {
                a.recycle();
            }
        }
    }

至於成員變數，這裡貼出所有成員變數，具體作用見註釋

/**
     * Logging tag.
     */
    public static final String LOG_TAG = "PathView";
    /**
     * The paint for the path.
     */
    private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    /**
     * Utils to catch the paths from the svg.
     */
    private final SvgUtils svgUtils = new SvgUtils(paint);
    /**
     * All the paths provided to the view. Both from Path and Svg.
     */
    private List<SvgUtils.SvgPath> paths = new ArrayList<SvgUtils.SvgPath>(0);
    /**
     * This is a lock before the view is redrawn
     * or resided it must be synchronized with this object.
     */
    private final Object mSvgLock = new Object();
    /**
     * Thread for working with the object above.
     */
    private Thread mLoader;

    /**
     * The svg image from the raw directory.
     */
    private int svgResourceId;
    /**
     * Object that build the animation for the path.
     */
    private AnimatorBuilder animatorBuilder;
    /**
     * The progress of the drawing.
     */
    private float progress = 0f;

    /**
     * If the used colors are from the svg or from the set color.
     */
    private boolean naturalColors;
    /**
     * If the view is filled with its natural colors after path drawing.
     */
    private boolean fillAfter;
    /**
     * The width of the view.
     */
    private int width;
    /**
     * The height of the view.
     */
    private int height;

然後是一些getter和setter方法。

    /**
     * Set paths to be drawn and animated.
     *
     * @param paths - Paths that can be drawn.
     */
    public void setPaths(final List<Path> paths) {
        for (Path path : paths) {
            this.paths.add(new SvgUtils.SvgPath(path, paint));
        }
        synchronized (mSvgLock) {
            updatePathsPhaseLocked();
        }
    }

    /**
     * Set path to be drawn and animated.
     *
     * @param path - Paths that can be drawn.
     */
    public void setPath(final Path path) {
        paths.add(new SvgUtils.SvgPath(path, paint));
        synchronized (mSvgLock) {
            updatePathsPhaseLocked();
        }
    }
    /**
     * If the real svg need to be drawn after the path animation.
     *
     * @param fillAfter - boolean if the view needs to be filled after path animation.
     */
    public void setFillAfter(final boolean fillAfter) {
        this.fillAfter = fillAfter;
    }
    /**
     * Animator for the paths of the view.
     *
     * @return The AnimatorBuilder to build the animation.
     */
    public AnimatorBuilder getPathAnimator() {
        if (animatorBuilder == null) {
            animatorBuilder = new AnimatorBuilder(this);
        }
        return animatorBuilder;
    }
   /**
     * Get the path color.
     *
     * @return The color of the paint.
     */
    public int getPathColor() {
        return paint.getColor();
    }

    /**
     * Set the path color.
     *
     * @param color -The color to set to the paint.
     */
    public void setPathColor(final int color) {
        paint.setColor(color);
    }

    /**
     * Get the path width.
     *
     * @return The width of the paint.
     */
    public float getPathWidth() {
        return paint.getStrokeWidth();
    }

    /**
     * Set the path width.
     *
     * @param width - The width of the path.
     */
    public void setPathWidth(final float width) {
        paint.setStrokeWidth(width);
    }

    /**
     * Get the svg resource id.
     *
     * @return The svg raw resource id.
     */
    public int getSvgResource() {
        return svgResourceId;
    }

    /**
     * Set the svg resource id.
     *
     * @param svgResource - The resource id of the raw svg.
     */
    public void setSvgResource(int svgResource) {
        svgResourceId = svgResource;
    }
    /**
     * If the real svg need to be drawn after the path animation.
     *
     * @param fillAfter - boolean if the view needs to be filled after path animation.
     */
    public void setFillAfter(final boolean fillAfter) {
        this.fillAfter = fillAfter;
    }
    /**
     * Animate this property. It is the percentage of the path that is drawn.
     * It must be [0,1].
     *
     * @param percentage float the percentage of the path.
     */
    public void setPercentage(float percentage) {
        if (percentage < 0.0f || percentage > 1.0f) {
            throw new IllegalArgumentException("setPercentage not between 0.0f and 1.0f");
        }
        progress = percentage;
        synchronized (mSvgLock) {
            updatePathsPhaseLocked();
        }
        invalidate();
    }

然後通過一個函式進行路徑的更新

 /**
     * This refreshes the paths before draw and resize.
     */
    private void updatePathsPhaseLocked() {
        final int count = paths.size();
        for (int i = 0; i < count; i++) {
            SvgUtils.SvgPath svgPath = paths.get(i);
            svgPath.path.reset();
            svgPath.measure.getSegment(0.0f, svgPath.length * progress, svgPath.path, true);
            // Required only for Android 4.4 and earlier
            svgPath.path.rLineTo(0.0f, 0.0f);
        }
    }

接著就一大堆measure啊，draw啊

 @Override
    protected void onSizeChanged(final int w, final int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        if (mLoader != null) {
            try {
                mLoader.join();
            } catch (InterruptedException e) {
                Log.e(LOG_TAG, "Unexpected error", e);
            }
        }
        if (svgResourceId != 0) {
            mLoader = new Thread(new Runnable() {
                @Override
                public void run() {

                    svgUtils.load(getContext(), svgResourceId);

                    synchronized (mSvgLock) {
                        width = w - getPaddingLeft() - getPaddingRight();
                        height = h - getPaddingTop() - getPaddingBottom();
                        paths = svgUtils.getPathsForViewport(width, height);
                        updatePathsPhaseLocked();
                    }
                }
            }, "SVG Loader");
            mLoader.start();
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (svgResourceId != 0) {
            int widthSize = MeasureSpec.getSize(widthMeasureSpec);
            int heightSize = MeasureSpec.getSize(heightMeasureSpec);
            setMeasuredDimension(widthSize, heightSize);
            return;
        }

        int desiredWidth = 0;
        int desiredHeight = 0;
        final float strokeWidth = paint.getStrokeWidth() / 2;
        for (SvgUtils.SvgPath path : paths) {
            desiredWidth += path.bounds.left + path.bounds.width() + strokeWidth;
            desiredHeight += path.bounds.top + path.bounds.height() + strokeWidth;
        }
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(widthMeasureSpec);

        int measuredWidth, measuredHeight;

        if (widthMode == MeasureSpec.AT_MOST) {
            measuredWidth = desiredWidth;
        } else {
            measuredWidth = widthSize;
        }

        if (heightMode == MeasureSpec.AT_MOST) {
            measuredHeight = desiredHeight;
        } else {
            measuredHeight = heightSize;
        }

        setMeasuredDimension(measuredWidth, measuredHeight);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        synchronized (mSvgLock) {
            canvas.save();
            canvas.translate(getPaddingLeft(), getPaddingTop());
            final int count = paths.size();
            for (int i = 0; i < count; i++) {
                final SvgUtils.SvgPath svgPath = paths.get(i);
                final Path path = svgPath.path;
                final Paint paint1 = naturalColors ? svgPath.paint : paint;
                canvas.drawPath(path, paint1);
            }
            fillAfter(canvas);
            canvas.restore();
        }
    }

    /**
     * If there is svg , the user called setFillAfter(true) and the progress is finished.
     *
     * @param canvas Draw to this canvas.
     */
    private void fillAfter(final Canvas canvas) {
        if (svgResourceId != 0 && fillAfter && progress == 1f) {
            svgUtils.drawSvgAfter(canvas, width, height);
        }
    }

我們看到他重寫了onSizeChanged方法，首先判斷執行緒是否是null，如果不為null，則呼叫join方法,讓該thread執行完run方法裡面的東西后，再執行join()方法後面的程式碼。後面的程式碼就是起了一個執行緒獲取寬度，高度，路徑並更新路徑等資訊。

onMeasure()方法裡就是一些測量內容了。具體測量邏輯見原始碼。

onDraw()方法主要完成繪製，其實很簡單，就是在Canvas上畫圖，遍歷所有Path，畫在畫布上，畫完後呼叫了fillAfter方法，如果設定了svg資源，以及fillAfter 成員變數為true，動畫已完成，則會保持動畫

最後這個自定義View類裡使用了建立者模式進行建立路徑動畫，比如動畫的時間，插值器，延時，監聽器等等。

/**
     * Object for building the animation of the path of this view.
     */
    public static class AnimatorBuilder {
        /**
         * Duration of the animation.
         */
        private int duration = 350;
        /**
         * Interpolator for the time of the animation.
         */
        private Interpolator interpolator;
        /**
         * The delay before the animation.
         */
        private int delay = 0;
        /**
         * ObjectAnimator that constructs the animation.
         */
        private final ObjectAnimator anim;
        /**
         * Listener called before the animation.
         */
        private ListenerStart listenerStart;
        /**
         * Listener after the animation.
         */
        private ListenerEnd animationEnd;
        /**
         * Animation listener.
         */
        private PathViewAnimatorListener pathViewAnimatorListener;

        /**
         * Default constructor.
         *
         * @param pathView The view that must be animated.
         */
        public AnimatorBuilder(final PathView pathView) {
            anim = ObjectAnimator.ofFloat(pathView, "percentage", 0.0f, 1.0f);
        }

        /**
         * Set the duration of the animation.
         *
         * @param duration - The duration of the animation.
         * @return AnimatorBuilder.
         */
        public AnimatorBuilder duration(final int duration) {
            this.duration = duration;
            return this;
        }

        /**
         * Set the Interpolator.
         *
         * @param interpolator - Interpolator.
         * @return AnimatorBuilder.
         */
        public AnimatorBuilder interpolator(final Interpolator interpolator) {
            this.interpolator = interpolator;
            return this;
        }

        /**
         * The delay before the animation.
         *
         * @param delay - int the delay
         * @return AnimatorBuilder.
         */
        public AnimatorBuilder delay(final int delay) {
            this.delay = delay;
            return this;
        }

        /**
         * Set a listener before the start of the animation.
         *
         * @param listenerStart an interface called before the animation
         * @return AnimatorBuilder.
         */
        public AnimatorBuilder listenerStart(final ListenerStart listenerStart) {
            this.listenerStart = listenerStart;
            if (pathViewAnimatorListener == null) {
                pathViewAnimatorListener = new PathViewAnimatorListener();
                anim.addListener(pathViewAnimatorListener);
            }
            return this;
        }

        /**
         * Set a listener after of the animation.
         *
         * @param animationEnd an interface called after the animation
         * @return AnimatorBuilder.
         */
        public AnimatorBuilder listenerEnd(final ListenerEnd animationEnd) {
            this.animationEnd = animationEnd;
            if (pathViewAnimatorListener == null) {
                pathViewAnimatorListener = new PathViewAnimatorListener();
                anim.addListener(pathViewAnimatorListener);
            }
            return this;
        }

        /**
         * Starts the animation.
         */
        public void start() {
            anim.setDuration(duration);
            anim.setInterpolator(interpolator);
            anim.setStartDelay(delay);
            anim.start();
        }

        /**
         * Animation listener to be able to provide callbacks for the caller.
         */
        private class PathViewAnimatorListener implements Animator.AnimatorListener {

            @Override
            public void onAnimationStart(Animator animation) {
                if (listenerStart != null) listenerStart.onAnimationStart();
            }

            @Override
            public void onAnimationEnd(Animator animation) {
                if (animationEnd != null) animationEnd.onAnimationEnd();
            }

            @Override
            public void onAnimationCancel(Animator animation) {

            }

            @Override
            public void onAnimationRepeat(Animator animation) {

            }
        }

        /**
         * Called when the animation start.
         */
        public interface ListenerStart {
            /**
             * Called when the path animation start.
             */
            void onAnimationStart();
        }

        /**
         * Called when the animation end.
         */
        public interface ListenerEnd {
            /**
             * Called when the path animation end.
             */
            void onAnimationEnd();
        }
    }

SVG檔案的載入等工作都在SvgUtils類中完成。依賴了一個jar包，該工具類主要負責資原始檔的載入和初始化

構造方法是傳入一個畫筆

    /** 
     * Init the SVGUtils with a paint for coloring. 
     * 
     * @param sourcePaint - the paint for the coloring. 
     */ 
    public SvgUtils(final Paint sourcePaint) {
        mSourcePaint = sourcePaint;
    } 

資原始檔的載入

    /** 
     * Loading the svg from the resources. 
     * 
     * @param context     Context object to get the resources. 
     * @param svgResource int resource id of the svg. 
     */ 
    public void load(Context context, int svgResource) {
        if (mSvg != null) return;
        try { 
            mSvg = SVG.getFromResource(context, svgResource);
            mSvg.setDocumentPreserveAspectRatio(PreserveAspectRatio.UNSCALED);
        } catch (SVGParseException e) {
            Log.e(LOG_TAG, "Could not load specified SVG resource", e);
        } 
    } 

其餘的方法就是跟繪製有關了。有興趣自己去下原始碼看看。這裡不做展開了。

原始碼解析完畢後，我們使用一下這個庫。我們首先使用github上的svg檔案做測試。

在佈局檔案中新增程式碼

    <com.eftimoff.androipathview.PathView
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/pathView"
        android:layout_width="150dp"
        android:layout_height="150dp"
        app:svg="@raw/monitor"
        app:pathWidth="2"
        app:pathColor="#ff0000"
        />

然後就可以通過getPathAnimator方法獲得建立者物件，通過一系列的鏈式呼叫配置動畫，比如延時，動畫持續時間，插值器，監聽器，最後呼叫start開始動畫。

PathView mPathView= (PathView) findViewById(R.id.pathView);
mPathView.getPathAnimator()
.delay(1000)
.duration(3000)
.interpolator(new BounceInterpolator())
.listenerStart(new PathView.AnimatorBuilder.ListenerStart() {
    @Override
    public void onAnimationStart() {
        Log.e("TAG", "start");
    }
})
.listenerEnd(new PathView.AnimatorBuilder.ListenerEnd() {
    @Override
    public void onAnimationEnd() {
        Log.e("TAG","end");
    }
}).start();

最終效果就是這樣子

當然我們也可以使用svg檔案裡的顏色，讓它繪製完成後繪製最終真正的svg，可以加入以下程式碼

mPathView.useNaturalColors();
mPathView.setFillAfter(true);

最終效果如下

當然你可能想讓它停留在某個狀態點，你可以使用以下函式進行設定，引數值範圍為0到1

mPathView.setPercentage(0.8f);

甚至你可以不用svg檔案，你可以使用Path類

Path path=new Path();
path.moveTo(0.0f, 0.0f);
path.lineTo(length / 4f, 0.0f);
path.lineTo(length, height / 2.0f);
path.lineTo(length / 4f, height);
path.lineTo(0.0f, height);
path.lineTo(length * 3f / 4f, height / 2f);
path.lineTo(0.0f, 0.0f);
path.close();
mPathView.setPath(path);

還有List型別

List<Path> paths = new ArrayList<Path>();
//to do paths.add(path)
mPathView.setPaths(paths);

當然對於自定義屬性，也可以通過程式碼設定

mPathView.setPathColor(0x00ff00);
mPathView.setPathWidth(5f);
mPathView.setSvgResource(R.raw.logout);

最後貼一下svg的一些命令，每個命令都有大小寫形式，大寫代表後面的引數是絕對座標，小寫表示相對座標。引數之間用空格或逗號隔開

• M： move to 移動繪製點
• L：line to 直線
• Z：close 閉合
• C：cubic bezier 三次貝塞爾曲線
• Q：quatratic bezier 二次貝塞爾曲線
• A：ellipse 圓弧

詳解

• M (x y) 移動到x,y
• L (x y) 直線連到x,y，還有簡化命令H(x) 水平連線、V(y)垂直連線
• Z，沒有引數，連線起點和終點
• C(x1 y1 x2 y2 x y)，控制點x1,y1 x2,y2，終點x,y
• Q(x1 y1 x y)，控制點x1,y1，終點x,y
• A(rx ry x-axis-rotation large-arc-flag sweep-flag x y)
  rx ry 橢圓半徑
  x-axis-rotation x軸旋轉角度
  large-arc-flag 為0時表示取小弧度，1時取大弧度
  sweep-flag 0取逆時針方向，1取順時針方向
  

更多詳情請參考w3c